handling special characters in parameters with XMLHttpRequest

from frontend(javascript) with POST and other parameters with names like

"&password=" document.getElementById('password').value

I'm using HttpServletRequest.getparameter to get the parameter string of password like

string pswd = request.getparameter("password");

The code works fine with all passwords that have special characters except passwords like these qwe100%qwe, qwe198%qwe
When I pass those passwords, if I were to read username or other parameters sent along with password also results in exception[illegalArgumentException]
any help is appreciated..